Image forming apparatuses, such as copying machines, have conventionally been developed which can produce copy images of different colors by replacing developing units. However, the replacement of these units, in these apparatuses, is very troublesome.
Thereupon, a copying machine as shown in FIG. 1 has recently been proposed. In this machine, developing units 1, e.g., four in number, are first revolved around a common axis in parallel relation so that one of units 1 is selected for use. Thereafter, an electrostatic latent image on photosensitive drum 2 is developed by means of the selected developing unit.
Generally, in the copying machine, a space for developing units 1 is secured between optical system 4 for optically scanning the original on original table 3 and paper supply system 5 for supplying copying sheets P. The space is fanned out from photosensitive drum 2. Therefore, if units 1 are revolved around center A in a position closer to drum 2, they interfere with optical system 4 and paper supply system 5 at regions 6 and 7, respectively.
Conventionally, in replacing developing units 1, they are first slid horizontally to a position remoter from drum 2, and then revolved around center B.
In this case, however, the replacement requires a mechanism for horizontally sliding the relatively heavy developing units. Thus, the apparatus must be provided additionally with a strongly-built, complicated mechanism, such as slide rails, parallel motion mechanism, etc.